The present invention relates to a fuel injection pump for internal combustion engines and, more particularly, to a fuel injection pump having a prestroke control mechanism.
In recent years, for the purposes of improving the fuel consumption rate of an internal combustion engine and reducing toxic ingredients in the exhaust gases a fuel injection pump has been proposed in which a control sleeve is fitted about a plunger and is axially moved by a control rod to vary the prestroke of the plunger, so that the position of a cam profile of a camshaft used when the fuel is pressure delivered is changed to vary the sliding speed of the plunger, to thereby vary the fuel injection rate. Such fuel injection pump is disclosed, for example, in Japanese Provisional Utility Model Publication (Kokai) No. 61-5366.
In the conventional fuel injection pump described above, as shown in FIG. 1 of the accompanying drawings, a device for supporting the control rod which moves the control sleeve is constructed such that reduced-diameter portions 31a and 31b of the control rod 31 at opposite ends thereof are respectively inserted in and supported by bores in respective bushes 30 and 30 which are respectively tightly fitted in fitting bores 29 and 29 formed respectively in opposite end walls of a pump housing 1.
In view of the function of the control rod, it is required for the control rod to have no radial and axial plays. To eliminate the radial play, it is desirable to diminish clearance e.sub.1 and e.sub.2 between thes respective bores in the two bushes 30 and 30 at the opposite ends and the reduced-diameter portions 31a and 31b of the control rod 31. However, if the clearances e.sub.1 and e.sub.2 are excessively diminished, there would be a fear that the control rod 31 cannot be fitted into the two bushes 30 and 30 because a slight eccentricity or inclination of the bores. For this reason, it is required to enhance the machining accuracy of the component parts, resulting in increase in the cost. Further, if respective axial clearances k.sub.1 and k.sub.2 between the axial end faces of the respective bushes 30 and stepped portions 31c and 31d of the control rod 31 are reduced so as to reduce the axial play, the axial clearances k.sub.1 and k.sub.2 during the engine operation vary greatly from those during the cooling condition of the engine, because of a difference in material therebetween. Therefore, there would be a fear that the axial clearances are lost during the cooling condition of the engine so that the control rod cannot move angularly. The defect due to the eccentricity of the bores in the respective bushes 30 can be eliminated by the use of an eccentric bush as disclosed in, for example, Japanese Provisional Utility Model Publication (Kokai) No. 51-85118. However, such eccentric bush cannot cope with the axial play.